KpOmpA and flagellin synergize with cytokines in inducing IFN-γ production by NK cells. Freshly isolated CD56⁺ (A-C) and CD56^dim and CD56^bright NK cells (D) were unstimulated or were stimulated with 1 μM KpOmpA, flagellin, or TT in the absence or in the presence of 5 ng/mL IL-1β, IL-12, or IFN-α, 2 ng/mL IL-15, or 200 U/mL IL-2 (A); or 8 to 200 U/mL IL-2 (B), 0.04 to 1 pg/mL IL-10 (C), or 200 U/mL IL-2 or 1 pg/mL IL-10 (D). Results obtained from freshly isolated CD56⁺CD3⁺ cells are also presented (E). After 48-hour incubation, IFN-γ levels were determined using ELISA, and results are expressed in ng/mL as mean ± SD (n = 5).